A novel monocarboxylate transporter 8 gene mutation as a cause of severe neonatal hypotonia and developmental delay
Anastasios Papadimitriou1, Alexandra Mihaela Dumitrescu, Antigone Papavasiliou
1Pediatric Endocrinology Unit, Third Department of Pediatrics, University of Athens School of Medicine, Attikon University Hospital, Rimini 1, Haidari, Athens 124 62, Greece. anpapad@med.uoa.gr
Abstract:
Monocarboxylate transporter 8 acts as a specific cell membrane transporter for thyroxine and especially triiodothyronine into target cells. It is expressed in brain neurons and in many other tissues. The monocarboxylate transporter 8 gene resides on chromosome Xq13.2. An 11-month-old male infant was referred because of severe hypotonia from early life and global developmental delay. Thyroid-function tests showed normal thyrotropin levels and the characteristic for the disorder, including high serum triiodothyronine and low thyroxine concentrations. Molecular analysis of the monocarboxylate transporter 8 gene showed that the patient was hemizygous for a novel missense mutation P537L. This case highlights the importance of determining thyroid hormone levels, especially triiodothyronine, in infants with severe neonatal hypotonia.
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